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The World's Longest Laser Created
Date: Friday, February 10, 2006 @ 01:30:21 EST

New Scientist

AN OPTICAL fibre 75 kilometres long has been transformed into the world's longest laser, a feat its inventors hope will improve long-distance transmissions.

Because optical fibres lose 5 per cent of their power for every kilometre, the signal must be amplified. Now Juan Diego Ania-Castañón and his team at Aston University in Birmingham, UK, have dispensed with amplifiers by making the entire fibre behave like a laser.  Lasers inject light at each end which continually excites some of the fibre's atoms to a higher energy, so they emit photons of a longer wavelength.

These are reflected by mirrors at each end, resulting in a stable, uniform laser. As a result, signal strength is maintained as it passes down the fibre, staying well above the level at which noise starts to significantly interfere with it.

Source: New Scientist

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